Method for determining the advance ignition angle internal combustion engines ignition systems

ABSTRACT

A method for determining the ignition point in ignition systems for internal combustion engines, having integrated knock control, a basic ignition point being determined on the basis of measured operating parameters using a stored characteristic map. The knock control, after engine knock has occurred, determines a knock control ignition point, which is more retarded than the basic ignition point, the knock control ignition point, in response to knock-free combustions, being altered step-by-step so as to be more advanced. Furthermore, a torque interface is integrated, which on the basis of the operating parameters and/or the demands placed by the driver, determines a torque-optimized ignition point, and the knock control ignition point being the most advanced permissible ignition point which is issued by the control unit.

FIELD OF THE INVENTION

The present invention relates to a method for determining the controlledvariables of cyclically repeating processes in internal combustionengines.

BACKGROUND INFORMATION

From the Bosch combined ignition and fuel injection system Motronik(1987722011, KH/VDT-09.85-DE), control units having an integrated methodfor determining the ignition control variables are known. In thiscontext, the control unit, between two ignition processes, determinesthe controlled variables such as dwell angle and ignition angle orignition point from information such as load and engine speed,temperature setting and throttle valve setting. In this context, thecontrolled variables are determined by stored characteristic maps, thecharacteristic maps, for determining the ignition point, beingcalculated on the basis of experiments on an engine test stand. In themotor vehicle, this characteristic map is then optimized according tothe specifiable criteria such as fuel usage, exhaust gas and drivingperformance, and is then stored. On the basis of the current operatingparameters, the ignition point is then derived from the characteristicmaps and can be adjusted to various operating conditions. For example,during idling, the ignition can be set at favorable exhaust gas values,perfectly smooth running, and minimum fuel usage, whereas in a partialload running, the vehicle performance and the fuel economy are in theforeground. Adjusting the ignition point individually to each operatingcondition of the engine makes it possible to take account, to a highdegree, of the specific demands placed on the engine. In this context,it is possible to adjust the ignition point specifically to the actualdemands on the torque of the internal combustion engine through linkingup with a torque interface. Furthermore, it is known to integrate, inthe ignition control, a knock control which advances the ignition pointafter the occurrence of knocking and then, when the knocking has ceased,returns step-by-step to the map-controlled ignition point. Thus theknocking operation of the internal combustion engine is avoided, whichsignificantly increases the life expectancy of the internal combustionengine.

SUMMARY OF THE INVENTION

The method of the present invention for determining the ignition pointin ignition systems for internal combustion engines having integratedknock control has the advantage that in determining the ignition pointthe advantages of optimizing the ignition point in accordance with thesetpoint torque can be combined with the knock control. In this context,the ignition timing advance and the adaptation of the knock control areblocked if the ignition point is reduced by the torque interface, since,in this case, the ignition point issued has been determined not by theknock control but by the torque interface. Since this ignition point,issued by the torque interface, is more retarded than the ignition pointof the knock control, in this case the ignition timing advance of theknock control is advantageously frozen. Thus, even in the case ofintegrated knock control and torque optimization of the ignition point,the most knock-free operation possible of the internal combustion engineis assured.

In this way, the most retarded possible ignition point can beadvantageously derived from a characteristic map on the basis of theoperating parameters. In this context, the most retarded possibleignition point can be established in the characteristic map in a wayspecific to the application, or it can be determined as a function ofthe system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a program flowchart individual process steps for carryingout the method according to the present invention.

FIG. 2 shows, in an ignition point-time diagram, the relationships ofthe various ignition points to each other.

DETAILED DESCRIPTION

FIG. 1 shows the individual process steps of the torque-optimized knockcontrol of the present invention, the knock control being implemented inaccordance with individual cylinders and the basic ignition point ZWGRUbeing determined in a first process step 10 on the basis of operatingparameters such as engine speed n, temperature T, and pressure p, usinga stored characteristic map KF, so that the basic ignition point ZWGRUis a function of characteristic map KF. In one working step 11,depicting knock control KR, in response to detecting a knock KL after atriggered combustion, a correction value ΔZW-KR is determined, whichthen, in working step 12, is added to basic ignition point ZWGRU, thusyielding knock control ignition point ZW(KR)=ZWGRU+ΔZW-KR. This additivecorrection of the basic ignition point in the knock control retards theignition point, thus pulling it away from the knock limit.

This knock control ignition point ZW(KR) is now conveyed, on the onehand, via a torque interface MD to a limiting stage 13 and, on the otherhand, directly to limiting stage 13. The torque interface represents onebranch, which determines a torque-optimized ignition point ZW-MDirrespective of whether knocking has begun or not, on the basis of thecurrent operation conditions and the demands posed by the driver, forexample, a maximum load. Torque-optimized ignition point ZW-MD isconveyed to limiting stage 13, just as is the ignition point from knockcontrol ZW(KR). This limiting stage 13 limits the ignition point for thenext combustion within a permissible band, the most retarded permissibleignition point Zw_(ret), determined in a working step 14, being alsoconveyed to limiting stage 13. This most retarded permissible ignitionpoint Zw_(ret), in this context, is yielded, for example, by thespecifiable exhaust gas temperature limit. Furthermore, this mostretarded permissible ignition point Zw_(ret) can be derived from afurther characteristic map on the basis of the current operatingparameters. The most advanced permissible ignition point is thetorque-optimized ignition point ZW-Md, which is determined by the torqueinterface. Thus the most advanced permissible ignition point and themost retarded permissible ignition point are available to limiting stage13, so that the ignition point to be issued is within this band.

Subsequently, in working step 15, the ignition point determined in thismanner is issued and then in a query 16 is checked, as to whether in thetriggered combustion an engine knock KL has occurred. If this is thecase, then the yes-output leads to working step 17, which conveys thenecessity of retarding the ignition point to knock control 11, whichthen, as was already described above, determines a correspondingcorrection value for the next combustion in this cylinder. If noknocking has occurred, the no-output of query 16 leads to a query 17. Inquery 17, it is checked as to whether the torque-optimized ignitionpoint is more retarded than the ignition point of knock control ZW(KR).If this is the case, i.e., torque interface Md has reduced the torqueand has retarded the torque-optimized ignition point further than wasrequested by the knock control, then the yes-output of query 17 leads toworking step 18, which blocks the ignition advance of knock controlignition point ZW(KR), the blocking resulting from a step-by-stepreduction of correction value ΔZW-KR. This means that the momentarycorrection value ΔZW-KR is retained, which, at the same time, amounts toblocking the ignition advance of the adaptation. If it has beendetermined in query 17 that torque-optimized ignition point ZW-Md ismore advanced than the ignition point of knock control ZW(KR), then theno-output of query 17 is conveyed to working step 19, and a step-by-stepreturn of the knock control ignition point is permitted in the directionof the characteristic map ignition point.

In FIG. 2, the various ignition points are depicted over time. At timeto, basic ignition point ZWGRU and torque-optimized ignition point ZW-Mdare determined in the control unit. Since by time t₀ no engine knock KLhad yet occurred, the basic ignition point has not yet been corrected bya correction value of the knock control, or expressed differently,ΔZW-KR=0. In accordance with the request that the torque-optimizedignition point be within the limiting band of the most advanced and mostretarded permissible ignition points, in time period t₀ →t₁,torque-optimized ignition point ZW-Md is issued as the ignition point tothe corresponding cylinder. At time t₁, an engine knock KL begins in thecylinder, the basic ignition point being thus additively corrected by acorrection value ZW-KR that is set by the knock control. Since knockcontrol ignition point ZW(KR), determined in this manner, is moreretarded than torque-optimized ignition point ZW-Md, this knock controlignition point is first issued beginning at time t₁. After the ignitionpoint has been retarded in this way, the ignition point, after aspecifiable number of knock-free combustions by time t₂, is changedstep-by-step so as to be more advanced, towards the basic ignitionpoint. This occurs in that correction value ΔZW-KR, which is determinedafter the engine knock, is reduced step-by-step. By time t₃, knockcontrol ignition point ZW(KR) is more advanced, with respect to theabove dead center OT, than torque-optimized ignition point ZW-Md, sothat beginning at time t₃, torque-optimized ignition point ZW-Md isagain issued. The ignition advance of the knock control ignition pointis blocked, which means correction value ΔZW-KR is not reduced anymoreas long as torque-optimized ignition point ZW-Md is more retarded thanthe knock control ignition point. By time t₄, for example, a change inthe demands placed on the internal combustion engine has occurred, and anew torque-optimized ignition point ΔZW-KR is determined, which is moreadvanced in relation to the previous torque-optimized ignition pointΔZW-KR, and is even more advanced than knock control ignition pointZW(KR), because this knock control ignition point ZW(KR) is issued andat the same time the ignition advance is continued. By time t₅, therelationship of the torque-optimized ignition point to the knock controlignition point has reversed once again, so that the ignition advance isblocked once again and the torque-optimized ignition point is issued.

The evaluation as to whether the issued ignition point of the torqueinterface is more retarded or more advanced than the ignition pointvalue of knock control ZW(KR), has the consequence that it is possibleto generate a very precise estimate as to whether the existing knock hasarisen despite the knock control or because of the torque optimization.Thus an even better engagement with the torque behavior is possiblewhile at the same time preventing engine knock in the internalcombustion engine.

It should be stated, in principle, that the knock control ignition pointis issued, and only when the torque-optimized ignition point is moreretarded than the ignition point determined in the knock control path isthis torque-optimized ignition point issued.

What is claimed is:
 1. A method for determining an ignition point in anignition system of an internal combustion engine, the internalcombustion engine including an integrated knock control arrangement, themethod comprising the steps of:(a) determining a basic ignition point asa function of measured operating parameters using a storedcharacteristic map; (b) after an engine knock is detected, determining aknock control ignition point using the knock control arrangement, theknock control ignition point being more retarded than the basic ignitionpoint; (c) changing the knock control ignition point in a stepped mannerso as to be further advanced in response to a knock-free combustion; (d)determining a torque-optimized ignition point as a function of at leastone of the operating parameters and a driver-generated demand using anintegrated torque interface, the knock control ignition point being amost advanced permissible ignition point which is generated by the knockcontrol arrangement; and (e) if the torque-optimized ignition point ismore retarded than the knock control ignition point, blocking anignition advance of the knock control ignition point after theknock-free combustion.
 2. The method according to claim 1, furthercomprising the step of:(f) if the torque-optimized ignition point ismore retarded than the knock control ignition point, issuing thetorque-optimized ignition point.
 3. The method according to claim 1,further comprising the step of:(g) comparing the knock control ignitionpoint with the torque-optimized ignition point.
 4. The method accordingto claim 3, wherein step (b) further includes the substepsof:determining a correction value using the knock control arrangement;and generating the knock control ignition point by adding the correctionvalue to the basic ignition point.
 5. The method according to claim 4,wherein step (b) further includes the substep of:reducing the correctionvalue in a stepped manner to advance the knock control ignition point.6. The method according to claim 5, wherein step (b) further includesthe substep of:maintaining the correction value while thetorque-optimized ignition point is more retarded than the knock controlignition point.